Modeling and experimental analysis of thermocapillary effect on laser grooved surfaces at high temperature

Abstract Spreading behaviors of oil on laser grooved stainless steel 316L surfaces were studied theoretically and experimentally at high temperature with consideration of thermocapillary effect. A mathematic model of droplet spreading on grooved surfaces was developed taking into account of thermocapillary, groove capillary, thermal viscous effect and surface tension. Then, numerical analysis and experiments were carried out on laser grooved surfaces with different temperature gradient and change of droplet center temperature from 24 to 200 °C accordingly. It was shown that the present model agreed well with the experiment in predicting oil droplet thermocapillary spreading. The initial acceleration phase of oil spreading was proved more and more significant with temperature gradient increasing, producing maximum velocity form 5.8 to 15.93 mm/s with the increasing of temperature gradient from 0 to 3.72 °C/mm. Besides, the oil spreading in the opposite direction of temperature gradient was faster than that in the direction of temperature gradient, and the distance difference increased form 0.06 mm to 1.16 mm with the increasing of temperature gradient from 0.45 to 2.12 °C/mm after 1 s spreading, which illustrated that thermocapillary effect was gradually weakened with the corresponding temperature rising. Further, oil thermal viscous effect was proved as the main reason for this weakening. Groove capillary should be the active force for the directional spreading and even directing oil to high temperature regions, especially under high temperature gradient conditions.